In industrial processes such as hydrocarbon conversion processes chemical reactions take place in a reactor vessel containing a catalyst bed. A fluid is brought into contact with the bed by flowing it downward close to the walls of the reactor vessel and then inward into contact with the catalyst.
In one arrangement the fluid passes downward through perforated ducts and flows out of the perforations along the length of the duct and into contact with the catalyst. The ducts used heretofor have consisted of an elongated back plate which is secured to the inside wall of the reactor vessel and a perforated front plate which is concave in cross section. The front plate and back plate are joined along their sides to define a flow chamber.
Such ducts have certain disadvantages. The front plate is conventionally formed by rolling it. Conventional rolling procedures cannot reliably form a front plate having side edges lying on a straight line. Thus, it is difficult to join the front plate to the back plate. If they are sucessfully joined the duct will be stressed so that it will be structrually weak.